Human trunk strength profile in lateral flexion and axial rotation

To determine the functional capability in asymmetric trunk motion, isometric and isokinetic lateral flexion and axial rotation strengths of a normal and patient samples were measured. Seventy-three normal asymptomatic subjects (41 males and 32 females) and ten patients (9 males and 1 female) were tested.

The dual objectives of the study were to develop a database for isometric and isokinetic lateral flexion and axial rotation strength capabilities of a normal sample and to determine the functional impairment of a sample of patients.

More than 60% of low back injuries are associated with trunk twisting. Asymmetric motions are important risk factors. However, strength capability data for axial rotation are sparse and those for lateral flexion nonexistent.

To achieve the objectives of the study, two devices were designed and fabricated. Isometric lateral flexion was tested bilaterally in neutral posture and at 10 degrees, 20 degrees, and 30 degrees of lateral bending. Isometric axial rotation was tested bilaterally in neutral posture and at 5 degrees, 10 degrees, 15 degrees, and 20 degrees of axial rotation. Isokinetic lateral flexion and axial rotation strengths were tested bilaterally starting from the neutral posture.

The strength invariably declined progressively for all groups with increasing postural asymmetry. The strength in isokinetic activities ranged between 60% to 70% of the strength measured in isometric activities. All groups were significantly stronger in lateral flexion compared with axial rotation. The female sample ranged between 60% to 70% values of males for all activities studied. The patient group was weakest, ranging between 45% to 55% for isometric and 52% to 58% for isokinetic activities of their control group.